'\" te
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.TH LGRP_LATENCY 3LGRP "April 9, 2016"
.SH NAME
lgrp_latency, lgrp_latency_cookie \- get latency between two lgroups
.SH SYNOPSIS
.LP
.nf
cc [ \fIflag\fR... ] \fIfile\fR... \fB-llgrp\fR [ \fIlibrary\fR... ]
#include <sys/lgrp_user.h>

\fBint\fR \fBlgrp_latency_cookie\fR(\fBlgrp_cookie_t\fR \fIcookie\fR, \fBlgrp_id_t\fR \fIfrom\fR,
     \fBlgrp_id_t\fR \fIto\fR, \fBlgrp_lat_between_t\fR \fIbetween\fR);
.fi

.LP
.nf
\fBint\fR \fBlgrp_latency\fR(\fBlgrp_id_t\fR \fIfrom\fR, \fBlgrp_id_t\fR \fIto\fR);
.fi

.SH DESCRIPTION
.LP
The \fBlgrp_latency_cookie()\fR function takes a cookie representing a snapshot
of the lgroup hierarchy obtained from \fBlgrp_init\fR(3LGRP) and returns the
latency value between a hardware resource in the \fIfrom\fR lgroup to a
hardware resource in the \fIto\fR lgroup. If \fIfrom\fR is the same lgroup as
\fIto\fR, the latency value within that lgroup is returned.
.sp
.LP
The \fIbetween\fR argument should be set to the following value to specify
between which hardware resources the latency should be measured:
.sp
.in +2
.nf
LGRP_LAT_CPU_TO_MEM     /* latency from CPU to memory */
.fi
.in -2

.sp
.LP
The latency value is defined by the operating system and is platform-specific.
It can be used only for relative comparison of lgroups on the running system.
It does not necessarily represent the actual latency between hardware devices,
and it might not be applicable across platforms.
.sp
.LP
The \fBlgrp_latency()\fR function is similar to the
\fBlgrp_latency_cookie()\fR function, but returns the latency between the given
lgroups at the given instant in time. Since lgroups can be freed and
reallocated, this function might not be able to provide a consistent answer
across calls. For that reason, the \fBlgrp_latency_cookie()\fR function should
be used in its place.
.SH RETURN VALUES
.LP
Upon successful completion, the latency value is returned. Otherwise \(mi1 is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.LP
The \fBlgrp_latency_cookie()\fR and \fBlgrp_latency()\fR functions will fail
if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The specified cookie, lgroup ID, or value given for the \fIbetween\fR argument
is not valid.
.RE

.sp
.ne 2
.na
\fB\fBESRCH\fR\fR
.ad
.RS 10n
The specified lgroup ID was not found, the \fIfrom\fR lgroup does not contain
any CPUs, or the \fIto\fR lgroup does not have any memory.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Evolving
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.LP
.BR lgrp_children (3LGRP),
.BR lgrp_init (3LGRP),
.BR lgrp_parents (3LGRP),
.BR liblgrp (3LIB),
.BR attributes (7)
